Skip to main content

@babel/plugin-proposal-function-bind

Detail​

JavaScript
obj::func;
// is equivalent to:
func.bind(obj)

::obj.func;
// is equivalent to:
obj.func.bind(obj);

obj::func(val);
// is equivalent to:
func
  .call(obj, val)

::obj.func(val);
// is equivalent to:
obj.func.call(obj, val);

Example​

Basic​

JavaScript
const box = {
  weight: 2,
  getWeight() {
    return this.weight;
  },
};

const { getWeight } = box;

console.log(box.getWeight()); // prints '2'

const bigBox = { weight: 10 };
console.log(bigBox::getWeight()); // prints '10'

// Can be chained:
function add(val) {
  return this + val;
}

console.log(bigBox::getWeight()::add(5)); // prints '15'

Using with document.querySelectorAll​

It can be very handy when used with document.querySelectorAll:

JavaScript
const { map, filter } = Array.prototype;

let sslUrls = document
  .querySelectorAll("a")
  ::map(node => node.href)
  ::filter(href => href.substring(0, 5) === "https");

console.log(sslUrls);

document.querySelectorAll returns a NodeList element which is not a plain array, so you normally can't use the map function on it, and have to use it this way: Array.prototype.map.call(document.querySelectorAll(...), node => { ... }). The above code using the :: will work because it is equivalent to:

JavaScript
const { map, filter } = Array.prototype;

let sslUrls = document.querySelectorAll("a");
sslUrls = map.call(sslUrls, node => node.href);
sslUrls = filter.call(sslUrls, href => href.substring(0, 5) === "https");

console.log(sslUrls);

Auto self binding​

When nothing is specified before the :: operator, the function is bound to its object:

JavaScript
$(".some-link").on("click", ::view.reset);
// is equivalent to:
$(".some-link").on("click", view.reset.bind(view));

Installation​

npm install --save-dev @babel/plugin-proposal-function-bind

Usage​

babel.config.json
{
  "plugins": ["@babel/plugin-proposal-function-bind"]
}

Via CLI​

Shell
babel --plugins @babel/plugin-proposal-function-bind script.js

Via Node API​

JavaScript
require("@babel/core").transformSync("code", {
  plugins: ["@babel/plugin-proposal-function-bind"],
});

References​